1. Field of Invention
The present invention relates to a gas damper and in particular to a damper for regulating a purging airstream as it is directed into an electrostatic precipitator.
2. Description of the Prior Art
In the typical electrostatic precipitator used to remove fly ash and other particulates from the stack gases of an electrical power plant, the discharge electrodes are suspended from a series of electrical insulators mounted on the roof of the precipitator. Each of the insulators is enclosed by a separate housing which is maintained at a pressure slightly above the pressure of the flue gases flowing through the precipitator to prevent an accumulation of the corrosive flue gases about the insulators. This is accomplished by directing a preheated purging stream of ambient air into each of the insulator housings through a series of ducts connected to a forced air blower mounted on the roof of the precipitator. While this type of arrangement protects the insulators from the corrosive flue gases, experience has shown that the air flow into the insulator housings must be very closely controlled. For example, if the flow rate is too low, the flue gases migrate into the insulator housings where they are cooled to the point that sulfuric acid and the like begins to condense out of the gases and collect on the insulators, or alternatively, if the flow rate is too high, the purging air tends to cool the interior of the precipitator which leads to a corrosive acid rain within the precipitator. In the past, it has been the practice to provide electronic sensors which measure the flue gas pressure in the interior of the precipitator and in turn signal an electrically actuated damper which adjusts the air flow accordingly. While this type of arrangement has proven to be satisfactory, it is expensive as well as being relatively difficult to adjust and repair in the field.